An ever increasing problem is that of pollution of electrical and electronic equipment by external or internal interference electromagnetic fields. For example, shielded cables for electronic equipment are frequently exposed to relatively large electromagnetic fields which induce unwanted signals in the shielded wires that can impair or even destroy the equipment connected to the cable. Accordingly, it desirable to reduce the shield currents and this is most effectively accomplished by grounding the shield at some convenient point prior to cable interconnection with equipment or entering shielded areas.
The grounding structure to which the cable shield is terminated may be a specially constructed housing for the equipment or other convenient means. Exemplary of the latter, on board a ship sensitive electronic equipment will frequently be stored below deck while cabling just as frequently must be located on deck where it is exposed to a variety of relatively large interference field sources (e.g., radar). In this case, termination of a cable shield would be to the ship deck or hull at the point where the cable passes through the deck to enter the ship interior.
A highly satisfactory termination means for this purpose is that disclosed in co-pending U.S. patent application Ser. No. 642,170, CABLE SHIELD GROUNDING APPARATUS, by M. K. Van Brunt, assigned to the same assignee as the present application. The grounding apparatus of this copending patent application is received on the cable with special means clampingly contacting the cable shield and the grounding apparatus is then securely affixed to the ship deck by welding, for example. The grounding apparatus of this patent application is one general class of apparatus and device that can be advantageously tested for shielding effectiveness by use of the fixture to be described.